Added jrnl formula

Hi there, 

I added a new formula for [jrnl](http://maebert.github.io/jrnl/) following your `contributing` guidelines.
It installs on a mavericks host and runs the test correctly.

If possible, please merge.

Thanks for your work.
What if the test sets ENV["XDG_CONFIG_HOME"] to testpath first? https://maebert.github.io/jrnl/advanced.html